4 I'AL.EOXTOLOGY OF OHIO. 



seai)ulas, tlr.^s i;iving us, as has been said, nearly the entire bony 

 structure. 



Since tliis inii)ortant discovery, Mr. Terrell has found a complete man- 

 dible and maxilhiry of larger size than any before met with; the mandi- 

 ble being twenty-two inches in length. 



From tliis rich array of material we get not only much additional light 

 in rei;ard tu the s,[v\n-t\ivc of Dinic/dhys, but are furnished .v-ib Dhe means 

 for accurately detiiiing the two known species of the genus. It also shows 

 that some eiTors were comniitted, from confounding tlie two species, in 

 writing the descriptions contained in Vol. 1. 



When the main portion of that volume was wi'itten, neither maxillary 

 nor mandilile had been found on the Lake Shore, ^ind all the bones of 

 Dinichthys collected at Sheffield, Monroeville, and Delaware, had been 

 grouped together under one specific name. 



In a. foot note appended to tlie description of Dinicldliys on page 322 

 of Vol. I., Part IL, is mentioned the discovery at Sheffield. I'y Prof. A. 

 A. Wright, of a mandible quite different from those found at Delaware. 

 This evidently belonged to a new species, to which the name Dinichthys 

 Tevrtlli was then attached. The large number of specimens since 

 obtained, and, indeed, all the remains of Dinichthys hitherto taken from 

 ■ the sununit of the Haron shale at Sheffield, belorig, as we now know, to 

 this species, which is quite distinct from that found at the base of the 

 formation at Delaware. Hence the Dorsal plate figured on Plate 32, 

 the Cranium on Plate 33, and the Supra-scapulas on Plate 34, Vol. I., 

 should be credited to Dlnichtliys Terrelli rather than to D. Hertzeri^ 

 with which they wxre formerly and erroneously connected. The details 

 of structure in which the species differ, will be given further^on. 



The study of the specimens, the discovery of wliich has been described, 

 has resulted not onl_y in abetter knowledge of the anatomy of Z^/^i^c/i^J/^y*, 

 but has revealed some interesting things in regard to the relations of this 

 genus to living and fossil fishes ; all of which will be briefly referred to in 

 the pages which follow. 



The most striking feature of DiniGhthys, apart from its great size, is 

 its dentition, of which we have now all the parts. In this the most con- 

 spicuous elements are the massive mandibles, of which the posterior 

 extremities are rounded and flattened, and wxre evi<lently connected witli 

 cartilaginous articular portions. The anterior end of each mandible is 

 turned up to form a strong, acute, and prominent tooth._ Behind this the 

 jaw is thickened by a ridge on the inside, M'hich usually terminates above 

 in a triangular, tooth-like projection. The upper margin of the mandible, 

 for five or six inches behind this projection, is compressed, and consists of 

 remarkably dense, enamel-like bone. In D. Ilertzeri this is produced 



